If the patient qualifies and consents to participate, an envelope will be opened that tells us to exchange the catheter for a new one OR infuse TPA (clot-dissolving drug) into the 2 ports for two and a half hours. Some dialysis patients have had a TPA "dwell" at the dialysis clinic to help increase blood flow during dialysis. The motion of the "infusion" of TPA is expected to be more effective than a "dwell" that sits still. Also, there is more TPA used during "infusion" than during the "dwell".